Single or multiple stage blower and nested volute(s) and/or impeller(s) therefor

ABSTRACT

A single ended or double-ended blower includes a blower motor assembly supporting opposed first and second shaft ends. The first and second shaft ends have respective first and second impellers attached thereto and enclosed within first and second volutes, respectively. The first volute is connected to an inlet and the second volute is connected to an outlet. The blower motor assembly is supported in a chassis enclosure. A radially outer inter-stage path is between the first and second volute. The second volute is at least partially substantially concentrically nested with the radially outer inter-stage gas path.

CROSS REFERENCE TO PRIORITY APPLICATIONS

This application is the U.S. national phase of International ApplicationNo. PCT/AU2006/001617, filed Oct. 27, 2006 which designated the U.S. andclaims the benefit of U.S. Provisional Application No. 60/730,875, filedOct. 28, 2005, U.S. Provisional Application No. 60/841,202, filed Aug.31, 2006 and U.S. Provisional Application No. 60/775,333, filed Feb. 22,2006, each of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for supplying breathablegas to a human, used in, for example, Continuous Positive AirwayPressure (CPAP) treatment of Obstructive Sleep Apnea (OSA), otherrespiratory diseases and disorders such as emphysema, or the applicationof assisted ventilation.

2. Description of Related Art

CPAP treatment of OSA, a form of Noninvasive Positive PressureVentilation (NIPPV), involves the delivery of a pressurized breathablegas, usually air, to a patient's airways using a conduit and mask. Gaspressures employed for CPAP can range, e.g., from 4 cm H₂O to 30 cm H₂O(typically in the range of 8-15 cmH₂O), at flow rates of up to 180 L/min(measured at the mask), depending on patient requirements. Thepressurized gas acts as a pneumatic splint for the patient's airway,preventing airway collapse, especially during the inspiratory phase ofrespiration.

Typically, the pressure at which a patient is ventilated during CPAP isvaried according to the phase of the patient's breathing cycle. Forexample, the ventilation apparatus may be pre-set, e.g., using controlalgorithms, to deliver two pressures, an inspiratory positive airwaypressure (IPAP (e.g., 4-8 cm H₂O)) during the inspiration phase of therespiratory cycle, and an expiratory positive airway pressure (EPAP(e.g., 10-20 cm H₂O)) during the expiration phase of the respiratorycycle. An ideal system for CPAP is able to switch between IPAP and EPAPpressures quickly, efficiently, and quietly, while providing maximumpressure support to the patient during the early part of the inspiratoryphase.

In a traditional CPAP system, the air supply to the patient ispressurized by a blower having a single impeller, i.e., a single stageblower. The impeller is enclosed in a volute, or housing, in which theentering gas is trapped while pressurized by the spinning impeller. Thepressurized gas gradually leaves the volute and travels to the patient'smask, e.g., via an air delivery path typically including an air deliverytube.

Other blowers utilize a pair of impellers with, for example, one oneither side of the motor but fixed to a common output shaft. Suchconfigurations are disclosed in commonly-owned U.S. Pat. No. 6,910,483and in commonly-owned co-pending application Ser. No. 10/864,869, filedJun. 10, 2004, each incorporated herein by reference in its entirety.

Single-stage blowers are often noisy and are not as responsive astwo-stage blowers in that they require longer periods of time to achievethe desired pressure. Two-stage blowers tend to generate less noisesince they can run at lower speeds to generate the desired pressure, andare more responsive. On the other hand, two stage or double-endedblowers tend to be too large for certain applications.

SUMMARY OF THE INVENTION

One aspect of the present invention relates generally to a single ormultiple stage, e.g., two or more stages, variable-speed blower assemblythat provides faster pressure response time with increased reliabilityand less acoustic noise, and in a smaller package.

Another aspect of the present invention relates to an impeller for usewith an blower assembly for the treatment of sleep disordered breathing.

To this end, the exemplary embodiments described herein have variousstructural aspects that are particularly advantageous. One aspectrelates to the blower motor assembly, and specifically, to theelimination of a typical motor housing, thus reducing both size andweight. With the elimination of the motor housing, the space between themotor body and the chassis in which the motor body is supported, definesthe first volute for pressurized air between the first and second stageimpellers.

In an embodiment, an annular dividing seal between the motor body andchassis divides the substantially radial space into two portions. Afirst or upper portion houses the upper half of the blower motorassembly and includes a gas inlet for supplying unpressurized gas to afirst stage impeller located at the upper end of the motor. The secondor lower portion houses the lower half of the blower motor assembly andincludes the first volute and a second gas inlet to a second stageimpeller located at the lower or opposite end of the motor. In otherwords, a first volute in the upper portion supplies gas to the secondinlet at the second stage impeller by means of an inter-stage path, anda second volute located within the motor body, and axially beneath thefirst volute, moves the air to the chassis outlet. This axially nestedarrangement of the volutes and the inter-stage path provides significantspace savings.

Another structural aspect of an exemplary embodiment relates to thesupport of the blower motor assembly on a plurality of springs withinthe chassis, providing vibrational isolation of the blower motorassembly from the chassis. Another related feature is the utilization ofa plastic material for the blower motor assembly top cover; a relativelysoft, flexible polymer, such as silicone rubber, for both the dividingseal between the blower motor assembly and chassis and for the couplingbetween the blower motor assembly outlet and the chassis outlet; andmetals such as aluminum or magnesium for the motor cap and motor body.The combination of dissimilar materials for various component partstends to damp out vibration and thus reduce noise.

In order to reduce inertia and thus enhance responsiveness in terms ofpressure variations, the first and second stage impellers are of thedouble-shroud type, but the pair of shrouds on the respective impellersare not identical. Rather, one shroud extends from a center hub of theimpeller a relatively short distance in a radially outward direction.The other shroud extends radially outwardly to the outer edges of theimpeller blades, but with a center opening having an inner diametersimilar to the outer diameter of the smaller shroud. This configuration,sometimes referred to herein as an “alternating shroud” configuration,facilitates manufacture and reduces inertia by reducing the amount ofmaterial in the outer portion of the impeller, without sacrificingimpeller rigidity requirements. This approach also reduces thesensitivity to variations in the gap between impeller and cover.

In another embodiment, nested volutes components are fastened togetherabout the blower motor, and are at the same time sandwiched betweenupper and lower lids or covers that may be snap-fit onto (or otherwisesuitably attached to) the respective volutes components, providing anaxially compact and easily assembled unit. This assembly is also adaptedto be received in a cup-shaped, open-ended flexible sleeve.

The impeller vanes or blades are continuously curved in a radialdirection, but also taper in width in the radially outer portions, alongedges adjacent the smaller-diameter shroud. Moreover, the outermosttransverse edges of the blades or vanes may be stepped along theirrespective transverse widths. This design reduces turbulence noise atthe tips of the blades and in addition, the impellers are preferablymade of a polypropylene rather than the conventional polycarbonate so asto provide even further acoustic damping properties.

In an alternative embodiment, the larger diameter shroud may have atruncated fiusto-conical shape, with a corresponding taper along oneedge of the impeller blades in a radial length direction, such that atleast the radially outer portions of the blades taper in width in aradially outer direction.

Another feature relates to having a matching taper along an adjacentsurface of the one or both of the top and bottom lids or covers toprovide a substantially constant distance between the tapered bladeedges and adjacent lid or cover surfaces.

Preferably, the first and second stage impellers are secured at oppositeends of the motor output shaft for rotation about a common axis. Theimpellers are placed in fluid communication with one another by the gasflow path such that they cooperatively pressurize gas in the first andsecond volutes before exiting the chassis outlet.

Accordingly, in one aspect, the invention relates to a double-endedblower comprising a blower motor assembly supporting opposed first andsecond shaft ends, the first and second shaft ends having respectivefirst and second impellers attached thereto and enclosed within firstand second volutes, respectively, wherein the first volute is connectedto an inlet and the second volute is connected to an outlet; and theblower motor assembly supported in a chassis enclosure; a radially outerinter-stage path between the first and second volute, wherein the secondvolute is at least partially substantially concentrically nested withthe radially outer inter-stage gas path.

In another aspect, the invention relates to a double-ended blowercomprising a blower motor assembly supporting opposed first and secondshaft ends, the first and second shaft ends having respective first andsecond impellers attached thereto; the blower motor assembly supportedwithin a chassis enclosure and comprising a motor body including abottom wall, a peripheral sidewall and a top cover and wherein the topcover is provided with a flexible seal that engages an inner wall of thechassis enclosure.

In another aspect, the invention relates to a blower comprising a blowermotor assembly supporting a shaft with a shaft end provided with animpeller, said impeller having a plurality of curved vanes, each vanetapering in width in radially outer portions thereof.

Another aspect of the invention is directed to an impeller comprising atop shroud; a bottom shroud; and a plurality of vanes extending from thetop shroud to the bottom shroud, each said vane including a top edge ata radially inner portion of the vane in contact with the top shroud anda bottom edge at a radially outer portion of the vane in contact withthe bottom shroud, such that a radially inner portion of the vane at thebottom edge of each vane is not in contact with or adjacent the bottomshroud and a radially outer portion of the vane at the top edge of eachvane is not in contact with or adjacent the top shroud.

In still another aspect, the invention relates to a double-ended blowercomprising: a blower motor including oppositely extending first andsecond shaft ends, supporting first stage and second stage impellers,respectively; first and second volute components on opposite sides ofthe motor and secured to each other; an upper lid or cover attached tothe first volute and a lower lid or cover attached to the second volute,the first volute component and the upper lid or cover defining a firstvolute in which the first stage impeller is mounted, the second volutecomponent and the lower lid or cover defining a second volute in whichthe second impeller is mounted, the first and second volutes connectedby a spiral inter-stage gas path substantially concentric with the firstand second shaft ends.

These and other aspects will be described in or apparent from thefollowing detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a blower motor assembly in accordancewith the first exemplary embodiment of the invention;

FIG. 2 is a perspective view of the blower motor assembly of FIG. 1, butrotated in a counter-clockwise direction about, a vertical center axisof the assembly approximately 90°;

FIG. 3 is another perspective view of the blower motor assembly as shownin FIG. 1, but with a top cover of the assembly removed;

FIG. 4 is a perspective view of a blower motor assembly in accordancewith another exemplary embodiment of the invention;

FIG. 5 is a an exploded perspective view illustrating the blower motorassembly of FIG. 4 in combination with a chassis;

FIG. 6 is a perspective view similar to FIG. 5, but with the blowermotor assembly inserted within the chassis;

FIG. 7 is a cross-section taken along the line 7-7 of FIG. 6;

FIG. 8 is a perspective view of an impeller of the kind incorporatedinto the blower motor assemblies shown in FIGS. 1 and 4;

FIG. 9 is a perspective view of the opposite side of the impeller shownin FIG. 8;

FIG. 10 is a section taken through line 10-10 of FIG. 9;

FIGS. 10-1 to 10-6 are views of an impeller according to anotherembodiment of the present invention;

FIGS. 10-7 to 10-10 are views of the impeller with three alternativeembodiments of the chamfering of the vane or blade tips;

FIG. 11 is a perspective view, partially in section, of the blower motorassembly and chassis, similar to FIG. 6 but with a top lid placed overthe chassis, and with part of the chassis and first stage impellerremoved;

FIG. 12 is a view of the blower motor assembly and chassis of FIG. 11,but from a slightly different perspective, and with supporting springsremoved for clarity sake;

FIG. 13 is a sectional view similar to FIG. 12 but with the blower motorassembly sectioned as well;

FIG. 14 is a plan view of the chassis, with the chassis lid and blowermotor assembly removed;

FIG. 15 is a bottom plan view of the blower motor assembly shown in FIG.4;

FIG. 16 is a perspective view of a flexible sleeve for use with a blowermotor assembly in accordance with another embodiment;

FIG. 17 is a top plan view of the sleeve shown in FIG. 16;

FIG. 18 is a side elevation of the sleeve shown in FIG. 17, sectionedalong line 18;

FIG. 19 is a bottom plan view of the sleeve shown in FIG. 16;

FIG. 20 is a perspective view, partially cut away, of the sleeve of FIG.16 assembled over a blower motor assembly;

FIG. 21 is a cross-section of a blower motor and sleeve assembly locatedwithin a chassis enclosure; and

FIG. 22 is a partial perspective of a variation of the flexible sleeveshown in FIGS. 16-21.

FIG. 23 is an exploded assembly view of a blower motor assembly inaccordance with another embodiment;

FIG. 24 is a section view of the assembled blower motor assembly of FIG.23;

FIG. 25 is a perspective view of a first volute component used in theembodiment illustrated in FIGS. 23 and 24;

FIG. 26 is a perspective view of assembled first and second volutecomponents from the embodiment illustrated in FIGS. 23 and 24;

FIG. 27 is a perspective view of the assembly of FIG. 26 but in aninverted position;

FIG. 28 is another perspective view of the assembled first and secondvolute components shown in FIGS. 26 and 27;

FIG. 29 is a perspective view similar to that shown in FIG. 28 butrotated approximately 180°;

FIG. 30 is a perspective view similar to FIG. 28 but with the assembledcomponents rotated slightly in a counterclockwise direction and tiltedto a more upright position;

FIG. 31 is a perspective view of the top lid or cover taken from FIG.23;

FIG. 32 is a perspective view of the top lid or cover of FIG. 31, butwith the lid or cover in an inverted position;

FIG. 33 is a perspective view of the bottom lid or cover taken from FIG.23;

FIG. 34 is a bottom plan view of the bottom lid or cover shown in FIG.33;

FIG. 35 is a perspective view of a flexible sleeve taken from FIG. 23;and

FIG. 36 is a another perspective view of the sleeve shown in FIG. 23.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

a) General

Referring initially to FIGS. 1, 2 and 3, a blower motor assembly 10 inaccordance with an exemplary embodiment generally includes a motor body12 having a top cover 14 and a bottom cover 16. The motor itself is ofconventional design and therefore need not be described in detail, otherthan to note that an output shaft (represented by center axis 48 in FIG.7) projects from opposite upper and lower ends of the motor but does notextend through the top and bottom covers 14, 16 of the assembly. In thisregard, it should be understood that references herein to terms such as“upper,” “lower,” “top” and “bottom,” etc. are for convenience only asviewed in connection with the drawings, and are not intended to belimiting in any way.

A gas inlet opening 18 is provided in the top cover 14 and a gas outlet20 is provided in a side wall of the motor housing 12. A power cable 22extends from the motor body for connection to a power source.

Before describing the blower motor assembly 10 in detail, reference ismade to FIGS. 5-7 and 11-14 that illustrate a chassis enclosure (orsimply, chassis) 24 that is adapted to receive the blower motor assembly10. More details of the chassis 24 can be found in U.S. patentapplication Ser. No. 10/533,840, filed May 4, 2005, incorporated hereinby reference in its entirety. More specifically, the blower motorassembly may be supported on a bottom wall 26 of the chassis 24 via aplurality of coil springs 28 (one shown in FIGS. 1, 2). Three suchsprings are employed in the exemplary embodiment but the number andarrangement of such springs may vary. Springs 28 are seated in pocketsor recesses 30 (see FIGS. 5 and 14) formed in the bottom wall 26 of thechassis 24, with the upper ends of the springs engaged in alignedsimilar pockets or recesses 31 in the underside of the bottom cover 16of the blower motor assembly 10 (see FIG. 15).

A gas inlet conduit 32 in chassis 24 (see FIG. 7) supplies gas to theblower motor assembly 10, while gas outlet tube 34 connects to the gasoutlet opening 20 of the blower motor assembly 10 when the latter isfully seated in the chassis.

The blower motor assembly 10 is preferably not enclosed within a typicalouter motor enclosure or housing. As a result, the blower motor body 12(FIGS. 1-3) itself is able to be installed within a smaller chassis,while maintaining a necessary gap between the motor body 12 and theperipheral side wall 36 of the chassis 24 for establishing thefirst-to-second stage gas path (as explained in further detail below).Note that wall 36 of the chassis 24 may be of double-wall construction(FIG. 7) or of single-wall construction (FIGS. 11-13). By supporting theblower motor assembly 10 on springs 28 (or other suitable vibrationdamping components), and spaced from the peripheral side wall 36 and lid38 of the chassis, the blower motor is vibrationally isolated from thechassis 24.

Upon insertion of the blower motor assembly 10 into the chassis 24, achassis lid 38 (FIGS. 7 and 11-13) is located over the blower motorassembly, closing the upper open end of the chassis.

With this general description in mind, the components as well as theoperation of the device will now be described in greater detail.

b) Blower Motor Assembly

It should be noted here that the blower motor assembly 10 shown in FIGS.1-3 is slightly different from the blower motor assembly 110 of FIGS.4-7 and 11-14. The assembly shown in FIGS. 1-3 is shown with variousdetails, some of which are related to manufacturing considerations thatmay or may not appear in the assembly shown in FIGS. 4-7 and 11-14 andvice versa, particularly with respect to the blower motor body, topcover and bottom cover. In this regard, the external component of theblower motor assembly in FIGS. 4-7 and 11-14 are designated by similarreference numbers as used in FIGS. 1-3, but with the prefix “1” added.To this extent, assemblies 10 and 110 may be considered differentembodiments although they are similar in terms of overall configurationand function. In addition, and, for purposes of this disclosure, theinternal components of blower motor assemblies 10 and 110 should beconsidered substantially identical.

With particular reference to FIGS. 7 and 11-13, the blower motorassembly 110 includes a motor body 112 formed with an interior chamber40 defined by a bottom wall 42 of the body 112, an inner side wall 44and a motor cap or end bell 46. The motor coil and armature (omitted forclarity) are secured within the motor body 112 in conventional fashionand an output shaft, shown schematically at 48, extends in oppositedirections through the motor cap 46 and the bottom wall 42 of the body112. The cap 48 and the bottom wall 42 may include suitable bearingsupports for the shaft. Note that the motor cap 46 engages an upperperipheral edge 52 of the motor body 112 and, via lateral flange 54 andvertical lip 56, engages an internal shoulder 58 of the top cover 114.The space 60 (also referred to herein as the “first volute”) between themotor cap 46 and the blower motor assembly top cover 114 is occupied bythe first stage impeller 62 that is secured to the upper end of themotor output shaft 48 via a center hub or bushing 50.

The blower motor body 112 is also formed with a depending skirt or outerwall 64 that is connected at its upper end to the inner side wall 44 bya generally horizontal flange 66. The flange 66 and thus the upper endof the outer wall 64 spirals downwardly about the inner side wall 44,forming the second stage volute (described further herein)—while thelower end of the outer wall 64 is engaged by the blower motor assemblybottom cover 116 by a telescoping fit indicated at 68. The space 70(also referred to herein as the “second volute”) between the bottomcover 116 and the bottom wall 42 of the blower motor body 112 isoccupied by a second stage impeller 72 that is secured to the lower endof the motor output shaft 48 via a center hub or bushing 75. The blowermotor body 112 and cap 46 are preferably made of aluminum or othersuitable heat conducting material for good thermal conduction, such asmagnesium. The heat conducting material can help to convectively coolthe motor and has good heat transfer characteristics. In addition, theheat taken away from the motor can be applied to heat the pressurizedgas traveling to the patient, e.g., via the air delivery tube.Alternatively, the heat can simply be diverted away from the motor andthe air delivery tube.

The top cover 114 of the blower motor assembly includes upper and lowerportions 74, 76, respectively. The upper portion may be constructed of arelatively rigid plastic or other suitable lightweight material and hasa generally inverted cup-shape, with a center opening or aperture 118through which air is supplied to the first stage impeller 62. The lowerportion 76 of the top cover is in the form of a depending skirt,attached to the upper portion 74 adjacent the shoulder or edge 58 byadhesive or any other suitable means. The lower portion 76 is preferablyconstructed of a flexible polymer or rubber material (e.g., siliconerubber) that enables the top cover 114 to seal against the innerperipheral wall 36 of the chassis 24 at 78. The significance of thissealing arrangement will be described further below.

The gas outlets 20 and 120, respectively, of the blower motor assemblies10 and 110 are also formed of a flexible material, such as siliconerubber. This results in a flexible sealed connection to the chassis gasoutlet tube 34 when the blower motor assemblies 10 or 110 are insertedand properly oriented within the chassis 24. The gas outlets 20, 120each include an outer oval-shaped peripheral rim 82, 182 and an inner,round rim 84, 184 define the outlet openings 86, 186 and that,respectively, are adapted to engage complimentary surfaces on the innerwall of the chassis 24, with rims 84, 184 specifically designed to besealably engaged by the round outlet tube 34 of the chassis.

c) Impellers

c1) First Embodiment—Alternating Double Shroud Impeller

The first and second stage impellers 62, 72 may be identical in design(though must be of mirrored geometry to suit the present embodiment)and, accordingly, only the impeller 62 will be described in detail. Withparticular reference to FIGS. 8-10, impeller 62 is of one-piece moldedplastic construction, although other suitable materials andmanufacturing techniques could be employed. The impeller 62 comprises aplurality of continuously curved or straight vanes or blades 88sandwiched between a pair of disk-like shrouds 90, 92. The smallershroud 92 incorporates the hub or bushing 50 that receives the upper endof the motor shaft 48. The shroud 92 overlaps an inner portion of thevanes 88, i.e., the outer diameter (OD) of the smaller shroud issubstantially smaller than the OD of the larger shroud 90. The latter isformed with a relatively large center opening 94, but this shroudextends to the radially outer tips of the vanes. Making the OD of thesmaller shroud 92 slightly smaller than the diameter of the centeropening 94 in shroud 90, facilitates the molding process used tomanufacture the impellers (by allowing the impeller to be easily mouldedin one piece).

By utilizing the differentially sized shrouds (specifically by havingonly one shroud in the outer portion of the impeller), the inertia ofthe impellers 62, 70 is reduced while the overall rigidity of theimpellers is maintained. In this regard, both impellers 62, 72 arepreferably constructed of a polycarbonate or polypropylene material (thelatter of which provides acoustic dampening properties that dampen theresonance of the impellers). Glass fibre reinforcement may be employedto increase the stiffness of the polypropylene or polycarbonate ifrequired.

The radially outer portions 96 of the vanes or blades 88 taper in widthand the transverse tip edges 98 may be stepped, as best seen in FIG. 10.Each vane may have a profile appropriate for the intended goal and suchprofile may be tapered. For example, each vane may taper in plan view(i.e., the edge thickness of each vane may taper from a larger width toa narrower width from inside to outside), and/or each vane may taper inelevation view (i.e., the height of each vane along the length may taperfrom a larger height to a smaller height from inside to outside). Thismay be achieved by tapering the vane or blade edges adjacent thesmaller-diameter shroud so that at least the radially outer portion ofthe blade tapers to a reduced width at the radially outer end of theimpeller. In addition, the cross-section thickness of the vanes may bevariable or tapered. These vane features are intended to reduce noise,and the stepped specifically function to break up pressure pulses aroundthe tips of the vanes. In alternative embodiment the trailing edges ofthe impeller blades may be disrupted by other disturbances, such as butnot limited to dimpling or roughening. Such disturbances break up thesmooth flow of air trailing off the blade edges and assist in reducingnoise.

In one embodiment, illustrated in FIGS. 10-7 to 10-9, the tip of theimpellers between the edge surface 88.3 which extends beyond the smallershroud 92 and the transverse tip edges 98 is chamfered or notched tocreate a transition surface 99 at the tip. Examples of this transitionsurface include a straight chamfer 99.1 (FIG. 10-7), a convex chamfer,for example arcuate 99.2 (FIG. 10-8), or a concave notch 99.3 (FIG.10-9).

The chamfer or notch dimension is preferably between 0.5-5 mm along eachedge (98 and 88.3), more preferably about 2 mm, from the notional cornerthat is formed by extending the planes of the transverse tip edges 98and the edge surfaces 88.3 to intersect, as shown in FIG. 10-10. Thedimension along each edge is not required to be the same.

The chamfering or notching of the blade as described is intended tofurther reduce noise, including decreasing the blade passing tones.

The exterior or outer surfaces of the bottom covers 16, 116 are alsoprovided with a plurality of fixed vanes 100 that may be arranged inthree sets of two as shown in FIG. 15, but other arrangements arecontemplated as well. These vanes serve to reduce the degree of swirl orspin of the gas before it flows gas into the second stage impeller 72 asfurther described herein.

c2) Second Embodiment—Tapered, Alternating Double Shroud Impeller

FIGS. 10-1 to 10-6 illustrate an impeller 62.1 according to analternative design of the present invention. Like impeller 62 shown inFIGS. 8-10, impeller 62.1 includes an alternating shroud design, but inaddition it is tapered in elevation view, e.g., the height of each vanevaries or tapers along its radial length as shown, for example, in FIGS.10-1 and 10-6. Each vane may also be tapered in widthwise direction, asseen in plan view. This tapered alternating shroud impeller combines theadvantages of an alternating shroud impeller (lower costs, lower inertiaand better balance) with the advantages of a tapered impeller (moreuniform radial air velocity through the impeller and hence lower noiseand higher efficiency). As a side benefit, the tapered alternatingshroud design also provides excellent stiffness and resistance tobending, drooping, or “creep”.

As noted above, impeller 62.1 has a tapered design and includes aplurality of continuously curved or straight vanes or blades 88.1sandwiched between a pair of disk-like shrouds 90.1, 92.1. Each vane88.1 includes a first edge 88.2 and a second edge 88.3. The radiallyouter portion 88.4 (FIG. 10-4) of each edge 88.2 abuts or is in contactwith or adjacent to an inside surface of shroud 90.1, while the radiallyinner portion 88.5 (FIG. 10-5) of the edge 88.2 of each vane extendsfurther radially inwardly beyond shroud 90.1 and is visible throughopening 90.2 (also referred to as the “small diameter” of shroud 92.1).Conversely, the radially inner portion of each edge 88.3 abuts or is incontact with or adjacent to an inside surface of shroud 92.1, while theradially outer portion of each edge 88.3 of each vane extends furtherradially outwards beyond shroud 92.1. and is visible in FIG. 10-1. Thetapered design is created in this example by forming shroud 90.1 in atruncated frusto-conical shape, while shroud 92.1 is generally planar(see FIG. 10-6). The vanes 88.1 between the shrouds are shaped to fit inthe space between the shrouds, such that the vanes gradually taper fromthe radially inner portion to the radially outer portion of the impelleralong the larger-diameter shroud.

The small and large diameters 90.2, 90.3, respectively, of the truncatedcone form a slanted wall 90.4 that is angled relative to shroud 92.1.The angle α is in the range of 0-60°, preferably between 10-30°,depending on the application. By contrast, the shrouds in FIGS. 8-10extend in generally parallel planes, although they may be of varyingthickness. The smaller shroud 92.1 incorporates the hub or bushing 50.1that receives the upper end of the motor shaft 48. The shroud 92.1overlaps an inner portion of the vanes 88.1, i.e., the outer diameter(OD) of the smaller shroud 92.1 is substantially smaller than the OD ofthe larger shroud 90.1. Shroud 90.1 is formed with opening 90.2 thatdoes not cover the radially inner portions of the vanes, but shroud 90.1extends to the radially outer tips of the vanes. Making the OD of thesmaller shroud 92.1 slightly smaller than the diameter of the centeropening 90.2 in shroud 90.1, facilitates the molding process used tomanufacture the impellers.

By utilizing the differentially sized shrouds (specifically by havingonly one shroud in the outer portion of the impeller), the inertia ofthe impellers 62.1 is reduced while the overall rigidity of theimpellers is maintained. In this regard, impeller 62.1 is preferablyconstructed of a polycarbonate or polypropylene material which providesacoustic dampening properties (the latter of which dampens the resonanceof the impellers). Glass fiber reinforcement may be employed to increasethe stiffness of the polypropylene or polycarbonate if required.

The radially outer portions 96.1 of the vanes or blades 88.1 may taperin width and the transverse tip edges 98.1 may be stepped, similar towhat is shown in FIG. 10-6 and/or notched or chamfered 99 as shown inFIGS. 10-7 to 10-10 and described above.

These vane features are intended to reduce noise, and stepped edgesspecifically function to break up pressure pulses around the tips of thevanes. In alternative embodiment the trailing edges of the impellerblades may be disrupted by other disturbances, such as but not limitedto dimpling or roughening. Such disturbances break up the smooth flow ofair trailing off the blade edges and assist in reducing noise.

Impeller 62.1 is also strong (higher rpms possible) and is even lowerinertia (faster response) and possibly quieter than impeller 62, whichis a generally parallel arrangement. Further, impeller 62.1 can be madein one piece due to its design.

The tapered alternating shroud embodiment is low cost and has goodbalance, very low inertia, low noise, and high strength. The use of atapered, shrouded design also involves less material usage. The tapereddesign can also result in more even gas velocity, e.g., velocity is keptconstant between the radially inner and outer ends of the vanes.

The gap between the top of the impeller and the top cover of a doubleshrouded impeller is not as sensitive to tolerances, compared to asingle shroud impeller. On single shrouded (or open) impellers, the topgap is very sensitive to variation, as the air can spill over the top ofthe blade if the top cover is relatively far away.

d) Volutes

Returning to FIGS. 7 and 11-13, it will be seen that the first volute isdefined by the space 60 (enclosing the first stage impeller 62 and alsoincluding an annular volute region immediately outward of the impeller)which is formed by the underside of the top cover 114 and the upper (orouter) side of the motor cap 46. After leaving the first volute 60 (ahigh velocity region), the air follows an inter-stage (i.e., astage-to-stage) path 102 which is a radially outer, downward spiral pathin the area between the outer peripheral skirt 64 of the blower motorbody 112 and the inner wall 36 of the chassis 24 leading to an inletopening 104 in the blower motor body bottom cover 116. This inletopening feeds the air pressurized by the first impeller 62 within thefirst volute 60 and transferred to the second stage impeller 72 and thesecond volute 70 via the inter-stage (stage-to-stage) path 102, with thegas flow into the opening 104 smoothed (deswirled) by vanes 100.

The second volute, as noted above, is defined by the chamber or space 70enclosing the second stage impeller 72 and continuing in an upwardspiral path between the outer and inner walls 64, 44, respectively, ofthe motor housing, leading to the gas outlet 20, 120.

It will be appreciated that having the inter-stage (stage-to-stage) path102 nested concentrically outside the first volute 60 and the secondvolute 70 provides considerable savings in the overall size of theblower motor assembly, thus enabling it to be installed in a smallerchassis.

The first and second volutes may have similar or different shapes.However, the first volute can be said to “ramp down”, while the secondvolute can be said to “ramp up”. Each ramp profile is preferably smooth,but each can also have a stepped gradient as well.

e) Operation

In operation, and using the embodiment or FIGS. 4-15 as an example, gas,typically air or oxygen, is supplied to the blower motor assembly 110via conduit 32 and hole 33. The air is then drawn in through inletopening 118 and into the first stage impeller 62. The impeller spins thegas and, in combination with the first volute 60 pressurizes the gas.After decelerating as it leaves the first volute, it flows in a downwardspiral on the inter-stage (stage-to-stage) path 102, moving into thespace between the motor body 112 and the chassis wall 36. Note that theseal at 78 between the motor body top cover 114 and the chassis wall 36prevents pressurized gas from escaping back into the nonpressurized areaabove the inlet opening 118. The flexible nature of the seal alsocontributes to the vibration isolation of the blower motor assemblyrelative to the chassis enclosure.

The gas, guided by fixed vanes 100, now flows into the second impeller72 which, in combination with the second volute 70, further pressurizesthe gas until it reaches the motor body assembly outlet 120 and exitsvia the chassis outlet tube 34.

While the blower described herein can be used for use in CPAP, NIPPV andBiLevel treatment of OSA, it should noted that the blower could alsoeasily be used or adapted for use with invasive ventilation as well.

f) Alternative Flexible Sleeve Embodiment

In an alternative arrangement, a blower motor assembly 200 (FIGS. 20,21), similar to the assemblies described hereinabove, is substantiallyenclosed by a cup-shaped, flexible sleeve 202, best seen in FIGS. 16-19.The sleeve 202 includes a peripheral side wall 204 and a bottom wall206. The bottom wall 206 of the sleeve may be formed with internalcurved vanes 208 that surround the second stage inlet opening of theblower motor assembly in a manner similar to the arrangement of vanes100 described above. The vanes 208 are preferably formed integrally withthe bottom wall 206, but could be separately applied, if desired, by forexample, a suitable adhesive. The vanes could also be formed on theunderside of the blower motor assembly bottom cover as in the previouslydescribed embodiments. A plurality of support feet 210 are shownintegrally molded within circular recesses 212 formed in the bottom wall232. Another support arrangement could be one large cylindrical web 211on the bottom outer face 233 of the sleeve, as shown in FIG. 22.

The peripheral side wall 204 of the sleeve 202 is substantially circularin cross-section, but with a pair of “flats” 214, 216 on either side ofan aperture 218 adapted to receive the gas outlet connector boss 220(see FIG. 20). The upper end of the sleeve may be formed with a reduceddiameter portion defining an upper rim 222 connected to the adjacentremaining sleeve portion by a radial shoulder 224. Note that the rim 222merges with the main portion of the sidewall 204 at the flats 214, 216such that the shoulder 224 terminates at locations 226, 228. Rim 222terminates at an internal, circular flange or lip 230 located radiallyinwardly of the rim 222. It will be appreciated that other equivalentattaching and/or sealing arrangements at the open end of the sleeve arewithin the scope of this invention.

When applied over the motor body as shown in FIGS. 20 and 21, the rim222 of the sleeve engages the peripheral rim of the top cover 232 in asnug, elastic fashion, with lip 230 seated in a circular groove 234 inthe cover. This elastic engagement provides a sufficient seal to preventescape of air/gas from the space between the motor body and the sleeve.

FIG. 21 illustrates the blower motor assembly located within a chassisenclosure 238. It will be appreciated that when pressurized gas/airflows between the stage 1 and stage 2 volutes radially between theblower motor assembly 200 and the flexible sleeve 202), the flexiblesleeve may be expanded radially outwardly into at least partialengagement with an interior wall 240 of the chassis enclosure 238. Inthis condition, vibrations will still be isolated by the air cushioninside the sleeve. In other words, the pressurized inter-stage gas/airthereby at least partially supports the blower motor assembly in amanner that isolates vibration while it also cushions the motor fromdamage during rough handling, transport, etc. In this regard, theresilient and flexible support feet 210 replace the springs 28, thuseliminating discrete components that can be difficult to handle andassemble.

A hole 236 in the shoulder 224 (FIG. 17) is utilized for wires connectedto the blower motor within the motor body. Alternatively, a notch couldbe provided in the upper lip or rim 222, opposite the aperture 218.

The flexible sleeve 202 may be made of any suitable flexible material,such as rubber, silicone, silicone rubber or a thermoplastic elastomer(TPE).

Incorporation of a flexible sleeve permits the size of the blower motorassembly to be reduced since the interstage air/gas now performs twofunctions in one space, i.e., the flowpath between stages and avibration isolating and bump cushioning element. In addition, the devicemay be made quieter since more space is made available to the inletmuffler volume. A further advantage is the elimination of the flexibleseal portion 76 of the top cover as described hereinabove.

g) Alternative Blower Motor Assembly Embodiment

FIG. 23 is an exploded view of another alternative embodiment of ablower motor assembly 242 including a first stage impeller 244associated with a first volute component (also referred to herein as amotor cap or end bell) 246 and a second stage impeller 248 associatedwith a second volute component (also referred to as the motor body) 250.The blower motor assembly is axially stackable so capable of automaticassembly. Additionally, the volute components are axially compact, andsandwiched between upper and lower lids as described below.

The first and second volute components 246, 250 are coupled togetherwith the motor M therebetween. For example, the first volute component246 may include a plurality of holes 252 to receive threaded screws 254for fastening the first volute component to the second volute componentprovided with aligned threaded holes for receiving the screws 254.Alternatively, or in addition, the second volute component 250 can beadhesively coupled to the first volute component 246, or the firstvolute component can be press fit onto the second volute component.

A rotor 256 of the motor is positioned within between volute components246 and 250, and the rotor includes a first shaft end 258 coupled to thefirst impeller 244 and a second axially aligned shaft end 260 coupled tothe second stage impeller 258. A top lid or cover 262 includes an inlet264 and is positioned over the first impeller, and a bottom lid or cover266 is positioned under and adjacent the second stage impeller 248. Thebottom lid includes a plurality of vanes 268 surrounding an inlet 270.Thus, the top lid or cover 262 in cooperation with the first volutecomponent 246 define a chamber or first volute 247 (FIG. 24) in whichthe first impeller 244 is located, while the lower lid or cover 266 incooperation with the underside of the second volute component 250defines, in combination with the lower lid or cover 266 another chamberor second volute 251, directly below a bottom wall 253 of the secondvolute component 250, in which the second impeller 244 is located. Aninter-stage gas path between the first and second volutes is describedin greater detail below.

A flexible motor sleeve 272 (FIGS. 23, 24, 35 and 36) surroundssubstantially the entire assembly, but includes a cut out portion 274 toreceive the outlet 276 of the second volute component 250. The sleeve272 is an elastomeric component that dampens vibration and/or resonanceof internal components. The use of the sleeve 272 may result in fewerparts as compared to common motor assemblies. The sleeve 272 may beinsert-molded onto aluminum, or it may co-molded onto the top and/orbottom lids.

FIG. 24 shows additional details of the motor M and its positionalrelationship to the first and second volutes. The motor M includes alaminated stack 278, a plurality of windings 280 and rotor magnet 282.The motor shaft 284 (which includes shaft ends 258, 260) is supported byupper and lower bearings 286, 288. Further, the volute components 246,250 are at least partially nested, which provides for a compact andspace saving design, particularly in the axial direction, while thesleeve 272 also helps conserve space in a radial direction. The sleeve272 is sealingly coupled to the motor assembly, e.g., using a thickenedportion 290 of silicone around its upper surface, as shown in FIGS. 24and 33, stretched about the edge of the upper lid or cover 262.

FIG. 25 shows the first volute component 246 with a part annular rampsurface 292 defining a flow channel 294 extending approximately 180°with increasing depth from an “inlet” end of the channel at 296 to an“outlet” end 298. FIGS. 26-30 illustrate the first and second volutecomponents 246, 250 in combination, without the motor. These figuresillustrate the inter-stage path of a gas (for example, air) as it ischannelled from the first impeller 244 to the second impeller 248, andhence from the first volute 247 to the second volute 251. Thisinter-stage path is generally concentric relative to the motor shaft 284and defines a transition zone designed to ramp downwardly in a spiralfashion from the first volute to the second volute. More specifically,the first two arrows in FIG. 26 lie on surface 292 of channel 294 in thefirst volute, and the third arrow lies on a more steeply-inclined rampsurface on the outside of the second volute component 250, which, inturn, continues along a substantially horizontal surface 302, also onthe second volute component 250.

This arrangement allows the gas to decelerate as it ramps down andexpands. Note that a groove 304 is now formed between surface 302 andthe underside of the first volute component 246. This groove is taperedin the circumferential direction, with surface 302 rising slightlytoward the first volute component 246 as best seen in FIGS. 28-30 so asto encourage forward and continued movement gas remaining in the firstvolute 246 and any decelerated gas in the inter-stage path, about thesecond volute component 250. A notch 255 in an inner wall 257 of thesecond volute component 250 permits passage of the motor wires (notshown).

In use, the gas spirals downwardly through the transitional zone andenters into the area 306 which also extends below the bottom lid orcover 266 and then into the opening 270 and into the second volute 251.Vanes 268 reduce the degree of swirl or spin as the gas flows to thesecond volute where the gas is then swirled about the volute 251 viasecond impeller 248 and upwardly to the outlet 276.

As shown in FIGS. 23 and 31 the top lid or cover 262 includes a flatupper surface 307 provided with the inlet opening 264 and a peripheraldepending skirt 308. An outlet hood 310 depends from a portion of theskirt 308 and covers the transition zone between the first and secondvolutes, allowing the gas to move radially outwards to fill thestage-to-stage or inter-stage path. Attachment tabs 312, 314 and 316serve to attach the upper lid to the underside of the first volutecomponent 246.

With reference to FIGS. 23, 24, 33 and 34, the bottom lid 266 is alsoformed with upstanding attachment tabs 314, 316, 318 on skirt 320adapted to engage a peripheral rim 322 on the second volute component250. With the first volute component 246 securely fastened to the secondvolute component 250 via screw fasteners 254, and with the upper andlower lids 262, 266 snap-fit onto, or otherwise attached to the firstand second volutes components, respectively, it will be appreciated thatassembly of the compact unit is easily achieved. The flexible sleeve272, best seen in FIGS. 23 and 24, 35 and 36 is telescopically receivedover the motor/volute assembly so as to further define the inter-stagegas path, as described above in connection with the embodimentillustrated in FIG. 21, and the manner in which the sleeved blower motorassembly described in connection with FIGS. 23-36 operates is otherwisesimilar to the embodiment shown in FIGS. 16-21.

With regard to the impellers 244 and 248, each of the blades may betapered towards the outside of the impeller, e.g., to axially move theblade tips from the cut-off to decrease the blade pass tone. Thisstructure may also maintain the cross-sectional area as moving out fromthe center of the impeller closer to constant. This will encourage theairflow to maintain contact with the blades, to increase efficiencyand/or decrease noise. In another variant, the surfaces of thecomponents adjacent the impellers could be tapered to match the impellershapes, thereby providing a constant distance between those surfaces andthe impeller blade edges. The impellers 244, 248 also have analternating shroud design as described above which can also help reducenoise.

The motor assembly thus described has a low inertia which may allow foruse in other applications, e.g., to respond quickly for other therapiesand/or to increase response of transducer(s). Further, the temperatureof the motor is cooler, and drag from the bearing heat is less due torunning the slower speeds of the motor, which helps with reliability.Also, the integrated volutes can help conduct heat into the air path towarm the air, which also has the effect of improving the reliability ofthe motor. Further, the generated heat can warm the air path, which canbe advantageous in cooler conditions. Another benefit is that there isless pressure across the bearings as a result of multistage air path.

h) Additional Features

In another variant, a mode of operation may be provided where the flowthrough the motor is intentionally oscillated to be faster than thebreathing rate. The results can be useful for diagnostic purposes, e.g.,to determine open or closed airway or for other diagnostic purposes.Suitable oscillation techniques are described in commonly owned U.S.Pat. No. 5,704,345. Such information can also be used to activate anactive vent.

A thermal cutout may be provided on the motor. The cutout would monitorthe heat in the motor casing, and shut off power in the event of anoverheat.

In another embodiment, the impellers could be structured to spin ineither the same directions or in opposite directions.

In yet another variant, the blower assembly could include a port forwater egress, such as holes at the bottom of the sleeve, to protectagainst water pooling at the bottom of the motor if it spills back froman attached humidifier.

Further, the motor housing body and the first and second volutecomponents may be integrated.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. For example, while many aspects of the inventionrelate to double ended or multi-stage blowers (two or more stages),single stage blowers are also contemplated. On the other hand, each endof the motor shaft may include multiple impellers. Also, the variousembodiments described above may be implemented in conjunction with otherembodiments, e.g., aspects of one embodiment may be combined withaspects of another embodiment to realize yet other embodiments. Further,each component or feature alone for any given embodiment may constitutean independent embodiment. In addition, while the invention hasparticular application to patients who suffer from OSA, it is to beappreciated that patients who suffer from other illnesses (e.g.,congestive heart failure, diabetes, morbid obesity, stroke, barriatricsurgery, etc.) can derive benefit from the above teachings. Moreover,the above teachings have applicability with patients and non-patientsalike in non-medical applications.

1. A double-ended blower comprising: a blower motor assembly supportingopposed first and second shaft ends, said first and second shaft endshaving respective first and second impellers attached thereto andenclosed within first and second volutes, respectively, wherein thefirst volute is connected to an inlet and the second volute is connectedto an outlet; and said blower motor assembly supported in a chassisenclosure; a radially outer inter-stage path between the first andsecond volute, wherein said second volute is at least partiallysubstantially concentrically nested within the radially outerinter-stage gas path.
 2. The double-ended blower of claim 1 wherein saidblower motor assembly is supported on a plurality of resilient membersand otherwise spaced from said chassis enclosure to therebysubstantially vibrationally isolate said blower motor assembly from saidchassis enclosure.
 3. The double-ended blower of claim 1 wherein saidblower motor assembly includes a motor body including a bottom wall, aperipheral sidewall, a motor cap and top and bottom covers, wherein saidfirst impeller is located in a first volute between said motor cap andsaid top cover, and said second impeller is located in a second volutebetween said bottom wall and said bottom cover.
 4. The double-endedblower of claim 3 wherein said second volute is located radially inwardof said inter-stage path.
 5. The double-ended blower of claim 4 whereinsaid first volute is located radially inward of said inter-stage path.6. The double-ended blower of claim 5 wherein said second volute islocated wholly within said motor body.
 7. The double-ended blower ofclaim 4 wherein an underside of said bottom wall of said blower motorassembly is provided with a plurality of fixed vanes for deswirling airentering the second volute.
 8. The double-ended blower of claim 3wherein said top cover is provided with an inlet opening for supplyingun-pressurized gas to said first impeller, said inlet opening in fluidcommunication with a gas inlet to said chassis enclosure.
 9. Thedouble-ended blower of claim 1 wherein said top cover is provided with aflexible seal that engages an inner wall surface of said chassisenclosure.
 10. The double-ended blower of claim 1, wherein each impellerincludes a plurality of vanes that taper in width in a radially outerportion thereof.
 11. The double-ended blower of claim 10 wherein eachvane has a stepped transverse edge at a radially outer end thereof. 12.A blower comprising a blower motor assembly supporting a shaft having atleast one shaft end provided with at least one impeller; said blowermotor assembly supported within a chassis enclosure and comprising amotor body including a first end wall, a peripheral sidewall and asecond end wall and wherein a flexible skirt forms a portion of saidsecond end wall and serves as a flexible seal that engages an inner wallof said chassis enclosure.
 13. The blower of claim 12 wherein saidblower motor assembly is supported on a plurality of resilient membersbetween said first end wall of the chassis enclosure and a bottom of theblower motor assembly.
 14. The blower of claim 13 wherein said pluralityof resilient members comprise a plurality of coil springs, each seatedin a respective pocket on first end wall of said chassis enclosure. 15.The blower of claim 12 wherein said flexible seal is composed of asilicone rubber material.
 16. The blower of claim 12 wherein said secondend wall further comprises portion of substantially rigid plasticmaterial.
 17. The blower of claim 12 wherein said blower motor assemblyis provided with a first gas inlet and a first gas outlet and whereinsaid chassis enclosure is provided with a second gas inlet incommunication with said first gas inlet and a second gas outlet incommunication with said first gas outlet, and wherein at least saidfirst gas outlet is formed of a flexible polymer material.
 18. Theblower of claim 17 wherein said chassis enclosure is constructed ofmetal.
 19. The blower of claim 18 wherein said motor body and an innercap are constructed of a heat conducting metal.
 20. The double-endedblower of claim 18 wherein each impeller is constructed of polycarbonatematerial.
 21. The double-ended blower of claim 18 wherein each impelleris constructed of polypropylene material.
 22. The blower of claim 12wherein said first end wall comprises a bottom end wall and said secondend wall comprises a top cover.
 23. A double-ended blower comprising ablower motor assembly supporting opposed first and second shaft ends,said first and second shaft ends having respective first and secondimpellers attached thereto; each impeller having a plurality of curvedvanes, each vane tapering in width in a radially outer portion thereof.24. The double-ended blower of claim 23 wherein each vane has a steppedtransverse edge at its radially outermost end.
 25. The double-endedblower according to claim 24 wherein said stepped transverse edgeincorporates a convex or concave notch.
 26. The double-ended bloweraccording to claim 23 wherein said blower motor assembly includes amotor body having a bottom wall and a cap, said first impeller locatedbetween said cap and a top cover, and said second impeller locatedbetween said bottom wall and a bottom cover.
 27. The double-ended bloweraccording to claim 23 wherein each impeller is formed with surfacedisturbances along trailing edges thereof.
 28. A double-ended blowerassembly comprising: a blower motor including oppositely extending firstand second shaft ends, supporting first stage and second stageimpellers, respectively; first and second volute components on oppositesides of the motor and secured to each other; an upper lid or coverattached to said first volute and a lower lid or cover attached to saidsecond volute, said first volute component and said upper lid or coverdefining a first volute in which said first stage impeller is mounted,said second volute component and said lower lid or cover defining asecond volute in which said second impeller is mounted, said first andsecond volutes connected by a spiral inter-stage gas path substantiallyconcentric with said first and second shaft ends, wherein each impellercomprises a first shroud; a second shroud, a plurality of vanesextending between the first shroud and the second shroud, each said vaneincluding a first edge at a radially inner portion of the vane incontact with the first shroud and a second edge at a radially outerportion of the vane in contact with the second shroud, such that aradially inner portion of the vane at the second edge of each vane isnot in contact with or adjacent the second shroud and a radially outerportion of the vane at the first edge of each vane is not in contactwith or adjacent the first shroud.
 29. The double-ended blower of claim28 wherein said upper lid or cover is provided with a gas inlet adjacentsaid first stage impeller and wherein said second volute is providedwith a gas outlet.
 30. The double-ended blower of claim 28 wherein saidplurality of vanes are curved, each vane tapering in width over aradially outer portion thereof.
 31. The double-ended blower of claim 28wherein each of said plurality of vanes has a width that isapproximately constant from the radially inner portion to the radiallyouter portion.
 32. The double-ended blower of claim 28 wherein each ofsaid plurality of vanes has an edge thickness and/or height that variesfrom the radially inner portion to the radially outer portion.
 33. Thedouble-ended blower of claim 32 wherein the edge thickness and/or heighttapers down from the radially inner portion to the radially outerportion.
 34. The double-ended blower of claim 28 wherein the firstshroud is of truncated frusto-conical shape, having a surface that isangled relative to the second shroud in the range of about 15-25degrees.
 35. The double-ended blower of claim 28 wherein an inter-stagegas path includes a ramped surface internal to said first volutecomponent which merges with a peripheral external surface on said secondvolute component.
 36. The double-ended blower of claim 35 wherein saidlower lid or cover is formed with an inlet for supplying gas from saidinter-stage gas path to said second volute.
 37. The double-ended blowerof claim 35 wherein said peripheral external surface on said secondvolute component forms one portion of a peripheral groove that tapers ina circumferential direction.
 38. The double-ended blower of claim 28wherein first shroud comprises a top shroud; said second shroudcomprises a bottom shroud; said first edge comprises a top edge; andsaid second edge comprises a bottom edge.